Electrolytic cell and process for electrolyzing sodium sulfate

ABSTRACT

An electrolytic cell comprising a housing having a parent solution chamber and a parent solution inlet, an anode compartment and a cathode compartment communicating with said chamber; said anode compartment having a porous (internal liquiddraining) anode mounted therein through which anolyte solution passes and an anolyte solution outlet; said cathode compartment having a porous (internal liquid-draining) cathode mounted therein through which catholyte solution passes and a catholyte solution outlet. The cell is particularly useful in electrolysis of sodium sulfate solution to form sulfuric acid and sodium hydroxide.

United States Patent Radd et al.

[ Sept. 23, 1975 ELECTROLYTIC CELL AND PROCESS FOR ELECTROLYZING SODIUM SULFATE FOREIGN PATENTS OR APPLICATIONS Inventors: Frederick J. Radd; Donald H.

Oertle, both of Ponca City, Okla.

Appl. No.: 394,698

ll/l924 Germany 204/283 Primary ExaminerR. L. Andrews Attorney, Agent, or FirmRonald J. Carlson ABSTRACT An electrolytic cell comprising a housing having a parent solution chamber and a parent solution inlet, an anode compartment and a cathode compartment com- 52] US. (:1. 204/98; 204/104; 204/263; municming with Said Chamber; said anode compart 204/264; 204/275; 204/276 ment having a porous (internal liquid-draining) anode [Sl] Int. Cl COld 1/06 mounted therein through which anolyte Solution [58] F'eld 0f search-w 204/263 275*2761 passes and an anolyte solution outlet; said cathode 204/1041 2831 284 compartment having a porous (internal liquiddraining) cathode mounted therein through which References Clted catholyte solution passes and a catholyte solution out- UNITED STATES PATENTS let. The cell is particularly useful in electrolysis of so- 1,019,969 3/1912 Lacroix 204/275 dium Sulfate Solution to form Sulfuric acid and Sodium 1,037,585 9/l9l2 Billiter r 1 204/283 hydroxi 2,273,036 2/1942 Heise et a]... 204/284 3,288,692 11/1966 Le Duc 204/263 10 Clam, 1 Drawmg Flgure ////1l///// ///77 2 j 22 T ly 4 z 5 a I. V 20 i /X/ l0 ELECTROLYTIC CELL AND PROCESS FOR ELECTROLYZING SODIUM SULFATE DISCLOSURE This invention relates to an electrolytic cell and a method for conveniently producing a separate electrolysisproduct solutions without'the necessity of employing ion permeable membranes or diaphragms;

Various electrolytic cells are known in the art which employ ion permeable membranes, eg US. Patv No. 3,523,880; US. Pat. No. 3,705,090; and US. Pat. No. 2,967,806. While such cells function adequately to produce separate electrolysis product solutions without mixing with the parent solution certain inherent maintenance disadvantages are present. Moreover, considerable power loss may occur across the membranes thus reducing the efficiency of the cells.

In accordance with this invention there is provided anelectrolytic cell of relatively simple construction for producing separate electrolysis product solutions without the necessity of employing ion permeable membranes. Briefly described, the cell comprises a housing having a parent solution chamber, a first. electrode compartment and a second electrode compartment, the first and second compartments being separated from each other but in communication with the parent solution chamber and vertically positioned relative thereto. Mounted within'the first and second electrode compartments are an anode and a cathode, respectively, each of which is porous to permit passage of a product solution therethrough, that is, porous in the sense of being internal liquid-draining.

As is apparent, the electrolytic cell of the invention operates to separated product solutions from the parent solution on a gravity basis. If the product solution being produced in a particular electrode compartment has a lower specific gravity than the parent solution the electrode compartment is located on the upper side of the housing and the product solution is then withdrawn through the corresponding porous electrode. On the other hand, if the electrode compartment for producing a product solution has a greater specific gravity than the parent solution such compartment would be located on the lower side of the housing with the product solution being withdrawn through its porous electrode. Obviously, depending upon the particular parent solution being processed the electrode compartment housing the anode and the electrode compartment housing the cathode may both be located in the upper side or the lower side of the housing or one may be located on the upper side with the other located on the lower side.

The electrolytic and process of the invention will be more fully understood by reference to the drawing wherein an embodiment of the electrolytic cell is depicted in cross section. This particular embodiment is for use in processing a parent solution wherein the product solutions have a higher specific gravity. It will be obvious to those skilled in the art that this embodiment may be easily modified to place one or both of the electrode compartments on the upper side of the cell depending on the relative specific gravity of the electrolysis product solution compared with the parent solution.

With reference to the drawing, there is provided a housing 1 defining a parent solution chamber 2, a first electrode compartment 3 and a second electrode compartment 4. Both electrode compartments are in communication with the parent solution chamber but are separated from each other by crotched portion 5 of the housing. Separation of the two electrode compartments so that there is no direct communication with each other is essential in the electrolytic cell of the invention so as to avoid intermingling of the product solutions produced at each electrode and permit their separate withdrawal as will be more apparent hereinafter. In other words, the electrode compartments must be so located with respect to each other that each is separated from the other by a boundary layer of parent solution.

The first electrode chamber 3 has mounted therein a porous anode 10 extending transversely across the chamber in juxtaposition with the side walls thereof. This anode is provided with a series of passageways 11 extending vertically therethrough and permitting fluid flow. The size of the passageways is not critical snice the flow rate of the product solution therethrough may be easily controlled by controlling the withdrawal rate using such means as valves, etc. It is also pointed out that while a solid porous anode has been illustrated it is possible that the anode may be formed from compacted adherent granules defining tortuous interstices extending through the anode which are capable of internal liquid-draining. In such instance, mesh supports may be employed for structural integrity. Such supports may be conductive or nonconductive. Other obvious constructions will occur to those skilled in the art to achieve the objective described above.

The materials used for the anode includes any conductive material which is inert to the parent and product solutions. Such materials may include graphite, lead, lead alloys of silver, antimony, tellurium, thallium, tungsten bronze, platinum, and the like.

The second electrode chamber 4 has mounted therein a porous cathode 20 extending transversely across the chamber and in juxtaposition with the side walls thereof. As illustrated, the porous cathode is a stainless steel screen although any conductive material resistant to the parent and product solutions may be employed such as copper, lead, lead alloys, nickel, iron, and the like. As with the anode, a variety of porous constructions may be used as will occur to those skilled in the art.

Each of the anode and cathode are provided with any suitable electrical leads as indicated which communicate with an electrical power source, all of which is known in the art.

It is emphasized that a concept of the invention resides in the use of at least one porous electrode as hereinbefore described and not in any particular construction of either the anode or cathode. Those skilled in the art will readily comprehend other obvious alternatives which may be used to achieve the same objectives aas the constructions described above.

While the porous anode 10 and porous cathode 20 may be used along in the respective electrode chambers 3 and 4, it may be desirable to employ porous covers 12 and 22 on the upper surface of the anode and cathode to aid in reducing back-mixing of the electrolysis product solutions with the parent solution due to gas generation which would have the effect of reducing efficiency of the cell. By way of example, these porous covers may be glass, cloth, sand, granular ceramics or plastic or other materials inert to the solutions in contact therewith.

While these porous covers may be of nonconductive materials certain additional advantages are achieved if they are formed of conductive materials such as pow dered or granular carbon. The same materials as the anode cathode in particulate, form may be used. This has the effect ofcxtending the surface area of the electrodes where electrolysis can take place thus making possible much smaller current densities per unit surface area fora given degree of electrolysis. This results in less gas generation and consequently less stirring action and resultant back-mixing. Increased electrode life should also be realized.

In order to aid the gravity separation of the electrolysis product solution from the parent solution in the electrode chambers porous hold-up layers 13 and 23 may also be employed, if desired, beneath the anode and cathode. These layers may be formed from inert nonconductive materials such as glass cloth, sand, plastic granules, plastic mesh or fibrous mat, or combinations of such materials. On the other hand, they may be of conductive materials as with the cover layers. Such layers permit the electrolysis product solutions to pass therethrough but at the same time serve to provide additional hold-up time to aid the gravity separation of the product solutions from the parent solution. These layers may be optimized relative to their permeability to aid in adjusting or controlling flow rates of the product solutions.

The housing 1 is also provided with an inlet 6 for introducing the parent solution to be electrolyzed to the cell. A vent 7 is also provided for the escape of any gases generated during electrolysis.

Each of electrode compartments 3 and 4 are provided with outlets 8 and 9 through which the electrolysis product solutions are withdrawn. These outlets may conveniently be provided with valves to control flow of the product solutions therethrough in conjunction with the hold-up layers described above. It should be understood that either or both the valves and permeability of the hold-up layers can be used for flow control.

The electrolytic cell of the invention has particular applicability in electrolytically processing an aqueous solution of sodium sulfate in aqueous sodium hydroxide and aqueous sulfuric acid solutions. This application has utility in an overall process for sulfur dioxide removal and recovery from flue gases such as described in U.S. Pat. No. 3,515,513 and U.S. Pat. No.

In describing the operation of the above-described electrolytic cell reference will be made to electrolyzing an aqueous solution of sodium sulfates although, as indicated previously, the electrolytic cell and process of the invention may be used to electrolyze various materials which form electrolysis product solutions having specific gravities different from their parent solution thus enabling gravity separation. The cell may be useful for ion removal from solution as in sea water desalination.

An aqueous sodium sulfate solution is'introduced to the parent solution chamber 2 of the cell by way of inlet 6. The rate at which the solution is introduced may-be such that a substantially constant level is maintained in the chamber or, on the other hand, periodic introductions of solution may be made so as not to let the solution level go below a certain level as necessary to carry out electrolysis. In situations Where one or both elec-' trode compartments are located on the upper side of.

the cell to accommodate product solutions which are lighter than the parent solution. the chamber 2 must be continuously maintained in a filled condition.

Under the influence of an impressed direct electric current, cations (sodium) of the electrolytic solution in the chamber pass toward the cathode compartment whereat they combine with hydroxide ions produced at the cathode by electrolysis of water to form an aqueous sodium hydroxide catholyte solution. Since the sodium hydroxide has a specific gravity greater than sodium sulfate the thus-formed catholyte solution settles downward through the porous cathode 20 and is withdrawn throughoutlet 9.

At the sametime. sulfate ions pass toward the anode compartment 3 whereat they combine with anodically produced hydrogen ions to form aqueous sulfuric acid anolyte solution. Due to its greater specific gravity and thus-formed anolyte solution settles downward through the porous anode l0 and is withdrawn through outlet 8.

Use of the porous cover 12 and 22 and the hold-up layers. 13 and 23 do not alter the above-described basic operation but will provide the additional benefits previously noted. v

The following examples will serve to further illustrate certain embodiments of the invention.

EXAMPLE 1 r In order to demonstrate the effectiveness of the electrode gravity separation concept for electrolytic cells, a beaker having an integral trough around its upper end and a capacity of about 500 ml was employed as the cell housing. Drains were attached to both the trough and the bottom portion of the beaker. For purposes of the demonstration, only the anode was constructed as a porous electrode. In this case, a half-inch thick graph? ite disc of about the same diameter as the beaker was perforated with a multiplicity of holes about 1/16 1/32 inch in diameter. The anode was mounted in the bottom portion of the beaker on supports so that it was positioned above the drain and was provided with a glass cloth cover on its upper surface. A simple steel ring positioned in the upper trough served as the cathode. Electrical leads were attached to both the anode and cathode.

An 0.5M aqueous Na SO solution having a pH of about 6.55 was introduced to the described cell to a level above the cathode ring and was maintained at that approximate level during the experiment by periodic addition of further 0.5M solution. Operation of the cell was begun by passing a current of about 500 milliamps (3 watts) to the electrodes and both catholyte and anolyte were withdrawn. The anolyte flow rate was set at about 10 ml/min. After about 50 minutes, the anolyte being withdrawn was determined to have a pH of about 2.8 indicating the presence of H The experiment was then terminated and the anolyte was titrated back to a pH of 6.55 with 0.1 normal sodium hydroxide to determine the equivalent H 80 formed. The efficiency of the cell was then determined to be about 6.25 watthours/g of H 80 EXAMPLE 2 A series of experiments were carried out using essentially a 3-inch diameter U-shaped inverted tube as the cell with the anode and cathode assemblies mounted in the legs. The cell arrangement was similar to that illustrated in the drawing. The anode and, the cathode assemblies were supported by rubber stoppers equipped with drain tubes and electrical leads The cathode assembly consisted of a glass wool layer on top of the rubber stopper sequentially followed by a porous hold-up layer of about /2 inch thickness. a stainless steel screen cathode (corresponding to about a number 60. USSS), and a porous cover layer. The materials used for the hold-up layer and cover layer and the thickness of the cover layer varied between some experiments although in all cases the material was the same for both layers.

The anode assembly consisted of a glass wool layer on top of the rubber stopper sequentially followed by a half-inch thick porous graphite anode having a multiplicity of 1/16 1/32 inch holes of A1 inch intervals extending therethrough, and a porous cover layer. The

material used for the cover layer was the same as and varied in the same manner as the cover layer of the cathode assembly.

In each experiment, the cell was initially filled with aqueous Na SO solution and some solution was intially drained through the anode and cathode assemblies. Power was applied through a full wave rectifier circuit (unfiltered) and measured with 21 Simpson Model 269 multimeter across the cell terminals and a Triplett Model 628 digital meter in series with the power supply. Pinch clamps were used on rubber tubing to adjust the anolyte and catholyte flow rates. With the power on and the anolyte flowing, the pH of the anolyte was monitored until near steady-state pH was achieved. Steady-state pH values for all the experiments were in the range of 2 to about 3 /2. At that time the anolyte sample was measured and back titrated to the original pH level of the Na SO solution to determine the equivalent H SO Using the results of the titration, length of sample collection time, volts and amps, calculations were made for cell efficiency in terms of watt-hours per g H 50 The details and results of these experiments are set forth in the following table.

Thus having described the invention in detail. it will be understood by those skilled in the art that certain variations and modifications may be made without departing from the spirit and scope of the invention as described herein and defined in the appended claims.

We claim:

1. An electrolytic cell comprising a housing having a parent solution chamber and a parent solution inlet. an anode compartment and a cathode compartment located separate from but adjacent to said parent solution chamber, each of said anode compartment and said cathode compartment being separated from each other and in direct communication with said parent solution chamber; said anode compartment having an anode mounted therein for generating an anolyte solu' tion and an anolyte solution outlet; said cathode compartment having a cathode mounted therein for generating a catholyte solution and a catholyte solution outlet; each of said anode and cathode being horizontally disposed within its compartment between said parent solution chamber and said respective anolyte or catholyte solution outlet and being porous so that the respective anolyte solution or catholyte solution may pass therethrough and be withdrawn from the electrolytic cell.

2. An electrolytic cell according to claim 1 wherein at least one of the porous anode or porous cathode is provided with a porous cover.

3. An electrolytic cell according to claim 2 wherein both the porous anode and porous cathode are provided with a porous cover.

4. An electrolytic cell according to claim 3 wherein the porous covers are of nonconductive material.

5. An electrolytic cell according to claim 3 wherein the porous covers are of conductive material.

6. An electrolytic cell according to claim 2 wherein the anode is graphite and has a carbon black cover layer.

7. An electrolytic cell according to claim 6 wherein the cathode is a stainless steel screen.

8. An electrolytic process which comprises introducing to an electrolytic cell a parent solution which upon electrolysis forms anolyte and catholyte solutions hav- TABLE Average Anolyte Efficiency, Test Na SO Flow, Electrode watt-hours/ No. Molarity cc/min Position Cover Layer Depth Volts Amps Ohms Watts gm H SO l 0.5 7.8 3 16" HAF Carbon Black 2 A" 8.8 0.500 17.6 4.40 5.95 2 0.5 8.0 3 /2" Ottawa Sand 3%" 14 0.485 28.9 6.80 10.00 3 0.5 10.7 A HAF Carbon Black, V2" 4 0.445 8.99 1.78 8.55 4 0.5 10.0 A" 5.7 0.540 10.6 3.08 13.3 5 0.5 8.2 34 34" 4.8 0.365 13.3 1.75 3.16 6 0.5 7.6 34" 7.2 0.735 9.8 5.29 5.07 7 0.5 7.8 A" 4.6 0.335 13.7 1.54 3.09 8 0.5 7.8 3.4 0.130 26.2 0.44 1.66 9 0.5 8.1 34" EDM Graphite Chips 92" 4.5 0.320 14.1 1.44 4.16 10 0.5 8.9 34" Above EDM $6" HAF 4.5 0.300 15.0 1.35 3.06 11 0.5 8.1 4.5 0.305 14.8 1.37 2.67 12 0.5 17.5 94" 4.7 0.325 14.5 1.53 3.07 13 0.5 15.5 A" 4.7 0.315 14.9 1.48 3.08 14 0.5 1.87 W4" 4.8 0.320 15.0 1.54 3.72 15 0.5 6.5 Activated Carbon", 4.5 0.335 13.4 1.51 6.22 16 0.5 7.5 14" HAF Carbon Black, 4.6 0.325 14.2 1.50 3.22 17 0.5 7.0 1 1" 4.6 0.315 14.6 1.45 3.07 18 0.5 3.1 14" 4.6 0.340 13.5 1.56 3.18 19 1.0 3.3 74" 4.1 0.360 11.4 1.48 3.14 20 0.1 5.5 A" 6.7 0.225 29.8 1.51 5.47 21 0.2 4.9 94" 5.6 0.270 20.7 1.51 3.95

""From top 01' center divider, e.g. element 5 of drawing ""Continental Carbon Company ""20+40 U.S Sieve Size ""crushed electrode s1ock. first '6 inch with 8+12. next V1 inch with l2+l6 "'Darco'G60 ing specific gravities different from the parent solution. subjecting the parent solution to electrolysis using an anode and a cathode, at-least one of said anode orcathode being porous whereuponthe thus-formed anolyte solution or catholyte solution gravitationally separates from the parent solution and passes through the-porous anode or porous cathode. respectively and separately recovering theanolyte solution or the catholyte solution. l g M .9. An electrolytic process according to claim 9 wherein both the anode and cathode are porous and UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 6 PATENT NO. 54

DATED Novem er 23, 1975 INVENTOR(S) Frederick R dd et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 6 delete "a" Column 1, line 34 delete "separated" and insert --separate-- Column 1, line 49 delete "in" and insert on-- Column 1, line 53 after electrolytic insert cell-- Column 2,v line 19 delete "snice" and insert --since-- Column 2, line 33 delete "includes" and insert ---include-- Column 2, line 57 delete "aas" and insert ---as Column 2, line 67 delete "glass," and'insert ---g1ass--- Column 3, line 7 after anode insert -and- Column 3, line 45 delete "in" and insert --into-- Colunm 4, line 19 delete "and" and insert --the--- Column 4, line 23 delete "cover" and insert --covers--- Column 5, line 18 delete "of" and insert -,-at-

Column 8, line 4 delete "7" and insert --9-- Signed and Scaled this Thirty-first Day of August 1976 AUCSI.

RUTH C. MASON C. MARSHALL DANN A! l 8 ff Commissioner oj'Parents and Trademarks 

1. AN ELECTROLYTIC CELL COMPRISING A HOUSING HAVING A PARENT SOLUTION CHAMBER AND A PARENT SOLUTION INLET, AN ANODE COMPARTMENT AND A CATHODE COMPARTMENT LOCATED SEPARATE FROM BUT ADJACENT TO SAID PARENT SOLUTION CHAMBER, EACH OF SAID ANODE COMPARTMENT AND SAID CATHODE COMPARTMENT BEING SEPARATED FROM EACH OTHER AND IN DIRECT COMMUNICATION WITH SAID PARENT SOLUTION CHAMBER, SAID ANODE COMPARTMENT HAVING AN ANODE MOUNTED THEREIN FOR GENERATING AN ANOLYTE SOLUTION AND AN ANOLYTE SOLUTON OUTLET, SAID CATHODE COMPARTMENT HAVING A CATHODE MOUNTED THEREIN FOR GENERATING A CATHOLYTE SOLUTION AND A CATHOLYTE SOLUTION OUTLET, EACH OF SAID ANODE AND CATHODE BEING HORIZONTALLY DISPOSED WITHIN ITS COMPARTMENT BETWEEN SAID PARENT SOLUTION CHAMBER AND SAID RESPECTIVE ANOLYTE OR CATHOLYTE SOLUTION OUTLET AND BEING POROUS SO THAT THE RESPECTIVE ANOLYTE SOLUTION OR CATHOLYTE SOLUTION MAY PASS THERETHROUGH AND BE WITHDRAWN FROM THE ELECTROLYTIC CELL.
 2. An electrolytic cell according to claim 1 wherein at least one of the porous anode or porous cathode is provided with a porous cover.
 3. An electrolytic cell according to claim 2 wherein both the porous anode and porous cathode are provided with a porous cover.
 4. An electrolytic cell according to claim 3 wherein the porous covers are of nonconductive material.
 5. An electrolytic cell according to claim 3 wherein the porous covers are of conductive material.
 6. An electrolytic cell according to claim 2 wherein the anode is graphite and has a carbon black cover layer.
 7. An electrolytic cell according to claim 6 wherein the cathode is a stainless steel screen.
 8. An electrolytic process which comprises introducing to an electrolytic cell a parent solution which upon electrolysis forms anolyte and catholyte solutions having specific gravities different from the parent solution, subjecting the parent solution to electrolysis using an anode and a cathode, at least one of said anode or cathode being porous whereupon the thus-formed anolyte solution or catholyte solution gravitationally separates from the parent solution and passes through the porous anode or porous cathode, respectively, and separately recovering the anolyte solution or the catholyte solution.
 9. An electrolytic process according to claim 9 wherein both the anode and cathode are porous and both the anolyte solution and catholyte solution gravitationally separate from the parent solution and pass through the porous anode and porous cathode.
 10. An electrolytic process according to claim 7 wherein the parent solution is sodium sulfate, the anolyte solution is sulfuric acid and the catholyte solution is sodium hydroxide. 